Backlight bleed test for LCD monitors.

How this test works

Use black and near-black fields in a dim room while viewing the screen from your normal position.

1. Prepare the display using the checklist below.
2. Select Start test and allow fullscreen mode if your browser asks.
3. Use the arrow keys, on-screen controls, or click the pattern to move through the test.
4. Exit the runner and save a local observation if useful.

Before you begin

• Dim the room
• Use a normal brightness setting
• Wait for the display to warm up

What to look for

• Bright patches near edges or corners
• Cloud-like uneven areas
• Changes caused by viewing angle

Use black and near-black fields on an LCD

This page is intended for displays with an LCD backlight. The runner shows pure black plus 1% and 3% gray fields. Let the panel warm up, use your normal brightness, dim the room without making it unrealistically dark, and inspect from your normal viewing position. Look for light that remains attached to an edge or corner, broad cloudy patches, or a glow that changes strongly as your head moves. OLED pixels emit their own light and have no LCD backlight, so an OLED dark-field concern calls for a different interpretation.

Pure black may make small variations more obvious than ordinary films or games. Compare the near-black fields as well and then check familiar dark content. A bright corner that is conspicuous only at maximum brightness in a dark room is a different practical issue from one that remains distracting at normal settings. Record which field reveals it and where it occurs. This visual comparison cannot quantify light leakage or decide whether the panel meets a manufacturer’s acceptance threshold.

Distinguish fixed edge leakage from viewing-angle glow

Backlight bleed is usually described as excess light near an LCD edge or pressure point. IPS glow is more dependent on viewing angle and often changes when you move your head relative to a corner. Broader clouding may sit away from the bezel. These labels are descriptions of appearance, not diagnoses that a browser can confirm. Keep the same brightness and room light while moving only your viewing position; if the region changes dramatically, note that rather than assigning a fixed-bleed label from one seated angle.

Automatic contrast, local dimming, and brightness controls can alter what a black field looks like. Compare with one feature changed at a time, then restore normal settings. Phone cameras often raise exposure on a dark scene, turning modest variation into a dramatic pale blotch. A photo can show the location but should not be used as a measured comparison with someone else’s picture taken under unknown exposure. Judge primarily with your eyes and describe the effect in ordinary use.

Know when another test is more useful

If the same patch is visible on middle gray or white, the screen uniformity page may better capture the wider variation. If a single bright point appears on black, use the dead pixel test to compare multiple solid colors. If you see a persistent interface outline on OLED, use the OLED retention page briefly and safely. These routes cover related but different shapes, technologies, and search questions. Using the relevant pattern helps you avoid describing every dark-screen observation as backlight bleed.

For a new LCD, note the panel model, brightness, viewing distance, room light, picture mode, and whether the glow is also distracting in normal content. Check the current return or support policy if it is. The browser cannot measure edge luminance, contrast ratio, or the mechanical cause of a bright region. It gives you a clean visual field and a way to repeat the observation. Do not press the bezel or panel to try to change a bright corner; that can damage the display and obscure the original issue.

Frequently asked questions